Using data from the 24,000 microscopically confirmed primary tumors (1,000,000 patient-years-at-risk) reported to the Veterinary Medical Data Program through June 1977, we expect to provide a reference of the distribution of spontaneous tumors in domestic animals. Further, using this relatively large series, we intend to search for unusual zoographic distributions of tumors, which may suggest possible clues regarding the etiology of cancer. The patient characteristics we expect to emphasize are age, breed/species, sex; the tumor characteristics are degree of malignancy, site and histogenic type. Only the bovine, equine, feline and canin species had a sufficient number of tumors reported to be of value in analytic studies. Currently conducting studies on multiple primary tumors, canine mammary tumors, and comparison of tumor occurrence reported by North American Veterinary Colleges with occurrence in Europe (reported to WHO).